Plywood and laminated veneer lumber are composite products formed by stacking thin sheets of wood veneer called plies. A sheet of plywood typically comprises a facing ply, a backing ply, and one or more core plies positioned between the facing ply and the backing ply. The core plies are not visible on the finished product, so they often are made of lower grade wood than the facing ply and the backing ply. Also, because the core plies are sandwiched between other plies, they do not need to be continuous. The core plies in many plywood products are formed from small pieces laid edge-to-edge. These pieces can be referred to as core pieces.
Plywood products typically are manufactured in standard sizes, such as 101 inches by 54 inches. Core plies matching the size of the desired product can be manufactured by lining up core pieces edge-to-edge to form a continuous sheet and then cutting that sheet into plies of a predetermined size. Some plywood manufacturing processes begin with a bottom layer of facing plies or backing plies lined up edge-to-edge. Each facing ply or backing ply is a continuous sheet with dimensions matching the dimensions of the desired final product. Adhesive, such as uncured phenolic resin, is applied to the bottom layer by one of a variety of methods (e.g., spraying, foaming, rolling or extruding). Core pieces then are placed edge-to-edge on the bottom layer. Adhesive is applied to each layer of core pieces before the next layer is added. After the final layer is added, the line of stacked plies is cut to size with a cross cut saw. The resulting sections are sent to a prepress where they are staged before entering a final hot press. In the final hot press, the stacked plies are heated and pressed to activate the adhesive and bond the plies.
Since core pieces typically have random lengths and must be cut into plies of a predetermined size, it is possible to have very narrow core pieces adjacent to the ends of the product before it is pressed. Sometimes, when the end pieces are very narrow, the adhesive is not strong enough to hold them in place. A plywood panel with a missing end piece is referred to as having a “narrow core.” Plywood panels with narrow cores are classified as “off grade” and are sold at lower prices than “on grade” panels.
Several references have suggested unifying the core pieces by various methods. For example, U.S. Pat. No. 1,977,199 discloses “passing the successive crossing strips, before they are coated with glue, through a machine which will fasten them together into one continuous sheet by gluing each strip to a pair of continuous strings or tapes . . . . ” See U.S. Pat. No. 1,977,199 at column 2, lines 68-76. Similarly, U.S. Pat. No. 4,044,182 discloses forming “veneer core blocks for plywood . . . by sewing green veneer strips which are closely contacted . . . or by affixing an adhesive tape on the surface of the closely contacted green veneer strips.” See U.S. Pat. No. 4,044,182 at column 1, lines 30-34.
The inventors of the present disclosure recognized, however, that the use of tape to unify core pieces is problematic in modern plywood manufacturing processes, which are designed for high-speed production. In most modern plywood manufacturing process, the core pieces are lined up by hand or by machine in a continuous stream. Due to a variety of factors, including human error, gaps can be created between the core pieces. These gaps can interfere with devices designed to apply tape continuously. For example, when a gap is encountered, a tape applicator designed to apply tape continuously might be damaged by contacting the underlying conveyor, particularly if the conveyor is a metal chain.
The inventors also recognized that applying tape to a continuously moving line of core pieces can cause the core pieces to overlap or become skewed. This typically occurs when the tape applicator interferes with the movement of the core pieces. Tape applicators apply at least some force to the core pieces, such as by rolling along the surface of the core pieces. When the force resisting movement of the core pieces is greater than the friction between the core pieces and the conveyor, the core pieces can be shifted out of alignment. Core pieces often are very thin, with a typical thickness being about one tenth of an inch, so they overlap easily. When one core piece is slowed or stopped by the tape applicator, the line will continue to move and the core pieces will begin to overlap. When the core pieces overlap, the process typically must be halted while the core pieces are realigned, resulting in lost production time and/or loss of product.
The inventors of the present disclosure recognized a need for tape application devices and methods that are compatible with continuous manufacturing processes. For example, the inventors recognized a need for tape application devices and methods capable of intermittent application of tape to continuously moving sheets of material. Such devices and methods were recognized as useful for a broad range of applications, including the effective processing of gaps between sheets of material to be joined.